Blocked polyisocyanate and uses thereof

ABSTRACT

Disclosed is a novel blocked polyisocyanate obtained by blocking the terminal isocyanate groups of a non-blocked polyisocyanate with a thermally dissociative blocking agent, wherein the non-blocked polyisocyanate is obtained by reacting at least one diisocyanate selected from the group consisting of an aliphatic diisocyanate and an alicyclic diisocyanate with a polyhydroxy compound having an average number of hydroxyl groups as many as 4.5 to 10, and removing substantially all unreacted diisocyanate monomers. A coating composition comprising the blocked polyisocyanate of the present invention as a curing agent and a polyol as a main agent not only has excellent curability even under low temperature conditions, but is also capable of forming a coating which has excellent impact resistance. The blocked polyisocyanate of the present invention has excellent miscibility with a plasticizer for the blocked polyisocyanate, so that, an adhesive property-imparting composition comprising the blocked polyisocyanate and a plasticizer and/or a solvent can be combined with a plastisol to prepare a plastisol composition having excellent adhesive properties even under low temperature conditions.

BACKGROUND OF THE INVENTION

1. Field of The Invention

The present invention relates to a novel blocked polyisocyanate and usethereof. More particularly, the present invention is concerned with anovel blocked polyisocyanate obtained by blocking the terminalisocyanate groups of a non-blocked polyisocyanate with a thermallydissociative blocking agent, wherein the non-blocked polyisocyanate isobtained by reacting at least one diisocyanate selected from the groupconsisting of an aliphatic diisocyanate and an alicyclic diisocyanatewith a polyhydroxy compound having an average number of hydroxyl groupsas many as 4.5 to 10, and removing substantially all unreacteddiisocyanate monomers; and is also concerned with use of the blockedpolyisocyanate.

The use of the blocked polyisocyanate of the present invention includes,for example, a coating composition comprising a polyol as a main agentand the blocked polyisocyanate as a curing agent; an adhesiveproperty-imparting composition comprising the blocked polyisocyanate,and a plasticizer and/or a solvent which are/is for the blockedpolyisocyanate; and a plastisol composition comprising a plastisol(which is a dispersion of a vinyl chloride polymer in a plasticizer) andthe adhesive property-imparting composition. The coating compositioncomprising the blocked polyisocyanate of the present invention as acuring agent has not only excellent curability even under lowtemperature conditions, but also is capable of forming a coating whichhas excellent impact resistance. Therefore, the coating composition ofthe present invention can be advantageously used for coating a metallicsubstrate (such as a steel plate or a surface-treated steel plate) and aplastic substrate, by the technique of roll coating, curtain flowcoating or the like. Especially, the coating composition of the presentinvention is useful as materials for undercoating, top coating andintercoating various substrates; a coating material for a precoatedmetal including a rust-resistant steel plate; and a coating material forimparting fine appearance, weatherability, acid resistance, rustresistance, mechanical strength (such as chipping resistance and impactresistance) and the like to automobiles. The blocked polyisocyanate ofthe present invention has excellent miscibility with a plasticizer forthe blocked polyisocyanate, so that, an adhesive property-impartingcomposition comprising the blocked polyisocyanate and a plasticizerand/or a solvent, can be combined with a plastisol to prepare aplastisol composition having excellent adhesive properties under lowtemperature conditions. This plastisol composition can be advantageouslyused, for example, as sealants, materials for forming an undercoatingand a chip-resistant coating, and a material for the preparation of aPVC-coated steel plate in the fields of automobiles, wherein theplastisol composition is applied to by the technique of spraying,brushing or the like.

2. Prior Art

Energy-saving and the prevention of air pollution are important tasks inthe field of coating. In this field, it has been desired to diversifyand improve the functions of coating compositions and plastisols.

A blocked polyisocyanate, which is obtained by blocking the terminalisocyanate groups of a non-blocked polyisocyanate derived from analiphatic and/or an alicyclic diisocyanate with a blocking agent, isstable at ambient temperature. However, upon heating the blockedpolyisocyanate, the blocking groups dissociate from the terminalisocyanate groups of the blocked polyisocyanate, and the resultantdeblocked polyisocyanate can serve as a curing agent for a polyol. Inview of the above-mentioned properties, the blocked polyisocyanate hasbeen expected to be a promising curing agent being capable of changingthe type of a polyurethane coating composition from a two-pack type to aone-pack type, wherein the polyurethane coating composition comprises apolyol as a main agent and the blocked polyisocyanate as a curing agent,and is capable of providing a coating having excellent properties, suchas chemical resistance, flexibility and weatherability. However, withrespect to the blocked polyisocyanate, it has been still desired toimprove the properties thereof, so as to not only solve theabove-mentioned tasks, but also diversify and improve the functionthereof.

With respect to the blocked polyisocyanate, which has conventionallybeen used as a curing agent for a one-pack polyurethane coatingcomposition, it is necessary to heat the coating composition to hightemperatures for releasing a blocking agent from the terminal isocyanategroups of the blocked polyisocyanate so as for the polyisocyanate tofunction as a curing agent. For example, when a coating is formed bybaking from a one-pack polyurethane coating composition comprising apolyol as a main agent and a blocked polyisocyanate as a curing agent,the baking must be conducted at a temperature as high as 150 to 200° C.Such a high baking temperature is disadvantageous in that not only doesit take a high cost to conduct the baking, but also a problem of airpollution is caused due to the high temperature baking. Such high bakingtemperatures cause difficult problems. For example, when a substratehaving a low heat distortion temperature (such as a plastic) is coatedwith the above-mentioned coating composition, a special jig device needsto be generally used in the baking procedure for preventing the heatdistortion of the substrate; however, in some cases, even such a specialjig device is not useful in the baking procedure.

Thus, the use of the conventional blocked polyisocyanate has beenlimited, and it has earnestly been desired to develop a novel blockedpolyisocyanate which can function as a curing agent for a polyol evenunder relatively low temperature conditions such that theabove-mentioned problems are not caused, that is, a temperature as lowas 110 to 130° C. (which is frequently desirable from a practical pointof view).

In these situations, several proposals have been made for lowering thebaking temperature necessary for curing the above-mentioned coatingcomposition, that is, for imparting the coating composition with acurability under relatively low temperature conditions (hereinafter,frequently referred to simply as "low temperature curability"). Forexample, for imparting a low temperature curability to a coatingcomposition there are some proposals of improving a curing acceleratorwhich is generally contained in the coating composition. As an improvedcuring accelerator, for example, Examined Japanese Patent ApplicationPublication No. 44-18877, Unexamined Japanese Patent ApplicationLaid-Open Specification No. 53-138434, Unexamined Japanese PatentApplication Laid-Open Specification No. 56-84714 (corresponding to G.B.Patent No. 2065151) and Unexamined Japanese Patent Application Laid-OpenSpecification No. 57-8217 (corresponding to G.B. Patent No. 2065151)disclose an organotin compound; Unexamined Japanese Patent ApplicationLaid-Open Specification No. 62-199609 discloses a lead compound, aninorganic zinc compound or a mixture thereof; and Unexamined JapanesePatent Application Laid-Open Specification No. 2-199112 discloses amixture of an organotin compound and at least one compound selected fromthe group consisting of a cobalt compound, a nickel compound and a zinccompound. However, a desired low temperature curability of the coatingcomposition cannot be achieved by improving only a curing accelerator.

As an alternative measure for imparting a low temperature curability toa urethane coating composition, there have been some proposals of usingan improved blocking agent for a non-blocked polyisocyanate. As animproved blocking agent, for example, Unexamined Japanese PatentApplication Laid-Open Specification No. 60-149572 discloses an alkylacetoacetate, Unexamined Japanese Patent Application Laid-OpenSpecification No. 6-287269 discloses a mixture of an oxime compound andan active methylene compound; Unexamined Japanese Patent ApplicationLaid-Open Specification No. 7-304843 (corresponding to Canadian PatentNo. 2148987) discloses a mixture of a triazol or a derivative thereofwith a pirazole or a derivative thereof; and Unexamined Japanese PatentApplication Laid-Open Specification No. 7-216051 (corresponding toCanadian Patent No. 2139365) discloses a pirazoline or a derivativethereof. However, these proposals concerning a blocking agent are alsounsatisfactory for achieving a low temperature curability of the coatingcomposition.

In addition to the above-mentioned methods in which it is attempted tolower a curing temperature for a urethane coating composition by usingan improved curing accelerator or an improved blocking agent, UnexaminedJapanese Patent Application Laid-Open Specification No. 6-293878(corresponding to International Patent Application Publication No. WO94/18254) discloses a method for lowering a curing temperature for aurethane coating composition by using as a curing agent amultifunctional polyisocyanate, i.e., a polyisocyanate having anisocyanurate skeleton, which has a number of terminal isocyanate groups.However, the curing agent used in this method is still unsatisfactoryfor avoiding the above-mentioned problems of a high cost for the bakingfor forming a coating, an air pollution caused by the baking and thelike, with respect to a polyester polyol, an epoxy polyol and the likewhich are used as main agents in urethane coating compositions.

In the field of coating, as mentioned above, it has also been desired todiversify the function of a coating composition. For example, in coldareas, especially North America and north Europe, rock salt and gravelare scattered on a road for the purpose of preventing the road fromfreezing. However, the scattered rock salt and gravel are caused to leapand fly by the turning wheels of cars, and such rock salt and gravelfrequently hit the cars, leading to various problems, such as occurrenceof scratches on car bodies. During wintertime in the cold areas, thetemperature frequently drops to -20° C. or lower. Under such lowtemperature conditions, coatings formed from conventional urethanecoating compositions do not absorb impact caused by rock salt andgravel. In these situations, it has been strongly desired to develop aonepack type coating composition which has not only a curability even ata temperature as low as 110 to 130° C. which is frequently desirablefrom a practical point of view, but also can provide a high impactresistance coating capable of protecting a car body from the impactcaused by rock salt and the like. However, no one-pack type urethanecoating composition having excellent impact resistance has beenreported.

In the field of coating compositions and sealants, a so-called plastisolwhich is a dispersion of a vinyl chloride polymer in a plasticizer isused. However, when a plastisol is coated on a metallic substrate, theplastisol does not exhibit satisfactory adhesion to the metallicsubstrate. Therefore, an improvement in adhesive property of theplastisol has been desired. Conventionally, for improving adhesiveproperty of a plastisol, an adhesive property-imparting composition isadded to the plastisol, which comprises a blocked polyisocyanate and/ora polyamide amine. With respect to the improvement in adhesive propertyby the use of the adhesive property-imparting composition, variousproposals have been made. As such an adhesive property-impartingcomposition, for example, Examined Japanese Patent ApplicationPublication No. 59-52901, discloses a polyamide amine and/or a blockedurethane prepolymer which is obtained by blocking the terminalisocyanate groups of a urethane type isocyanate prepolymer produced froma polyol and a diisocyanate with a blocking agent; Examined JapanesePatent Application Publication No. 62-41278 discloses a blockedpolyisocyanate obtained by blocking with a long-chain alkyl phenol apolymer of the diisocyanate, having an average molecular weight of from1,000 to 10,000; Unexamined Japanese Patent Application Laid-OpenSpecification No. 1-170633 discloses a polyamine and/or an urethane typeprepolymer of a blocked polyisocyanate having an isocyanurate skeleton;and Examined Japanese Patent Application Publication No. 3-29257(corresponding to U.S. Pat. No. 5,043,379) discloses a blocked polymerof an aromatic diisocyanate obtained using at least two types ofalkylphenol blocking agents. The polyamide amines and polyaminesproposed in the above documents have excellent adhesiveproperty-imparting ability. However, they have poor water resistance,yellowing resistance and the like. In addition, the above-mentionedblocked polyisocyanates have problems in that, although they haveexcellent water resistance, they are incompatible with a plasticizer fora vinyl chloride polymer plastisol and have unsatisfactory adhesiveproperties under low temperature conditions, and thus, the use of suchblocked polyisocyanates have been limited.

In British Patent No. 994890, a polyisocyanate obtained from a polyetherpolyol and a diisocyanate is disclosed. However, this document has nodescription or suggestion about a blocked polyisocyanate obtained byblocking the polyisocyanate, and a one-pack type coating compositioncontaining such a blocked polyisocyanate. Needless to say, this documenthas no description about the properties of the coating composition, suchas a low temperature curability.

Unexamined Japanese Patent Application Laid-Open Specification No.7-304724 (corresponding to Canadian Patent No. 2148783) discloses amethod for producing a polyisocyanate having an allophanate bond, inwhich a urethane bond-containing polyisocyanate (obtained by reacting apolyhydroxy compound with an aliphatic diisocyanate and/or an alicyclicdiisocyanate) is reacted with an aliphatic diisocyanate and/or analicyclic diisocyanate in the presence of a tin compound. Each of thepolyhydroxy compounds used in Examples of the above document has anaverage number of hydroxyl groups of only 1 or 2, and there is nodescription about a polyhydroxy compound having a large average numberof hydroxyl groups, such as an average number in the range of from 4.5to 10. Further, there is no description about the use and effects of aspecific blocked polyisocyanate obtained using as a modifier apolyhydroxy compound having such a large average number of hydroxylgroups.

Unexamined Japanese Patent Application Laid-Open Specification No.2-132116 (corresponding to U.S. Pat. No. 4,762,752) discloses apolyisocyanate having a relatively large average number of isocyanategroups. The average number of isocyanate groups per molecule of thepolyisocyanate is from 3 to 6. However, the polyisocyanates having anaverage number of isocyanate groups of 4 or more disclosed in theabove-mentioned document have aromatic isocyanate groups and hence havepoor durability.

SUMMARY OF THE INVENTION

The present inventors have made extensive and intensive studies with aview toward developing an excellent blocked polyisocyanate for use inpreparing a one-pack type polyurethane coating composition comprising apolyol as a main agent and a blocked polyisocyanate as a curing agent,which is free of the abovementioned problems accompanying theconventional curing agents. As a result, it has unexpectedly been foundthat a novel blocked polyisocyanate obtained by blocking the terminalisocyanate groups of a specific non-blocked polyisocyanate with athermally dissociative blocking agent (wherein the specific non-blockedpolyisocyanate is obtained by reacting at least one diisocyanateselected from an aliphatic diisocyanate and alicyclic diisocyanate witha polyhydroxy compound having an average number of hydroxy groups asmany as 4.5 to 10) does not cause a curing reaction at room temperaturebut is capable of causing a curing reaction even at a temperature in therange of from 110 to 130° C. (such a temperature is low as compared tothe temperature at which conventional one-pack type urethane coatingcompositions can be cured) which is frequently desirable from apractical point of view, and functions as an effective curing agent fora polyol under such low temperature conditions. It has also been foundthat a coating composition comprising a polyol as a main agent and theabove-mentioned novel blocked polyisocyanate as a curing agent not onlyexhibits excellent curability even under low temperature conditions, butis also capable of forming a coating which has excellent impactresistance; that the novel blocked polyisocyanate exhibits excellentcompatibility with a plasticizer and is capable of forming an adhesiveproperty-imparting composition comprising the blocked polyisocyanate anda plasticizer and/or a solvent; and that the adhesive property-impartingcomposition, when combined with a plastisol, is capable of providing aplastisol composition exhibiting excellent low temperature adhesiveproperties. The invention has been completed, based on these novelfindings.

Accordingly, it is a primary object of the present invention to providea blocked polyisocyanate which does not cause a curing reaction at roomtemperature but is capable of causing a curing reaction at such arelatively low temperature as is frequently desirable from a practicalpoint of view, and which can impart an excellent low temperaturecurability to a one-pack type coating composition comprising a polyol asa main agent and the blocked polyisocyanate as a curing agent.

It is another object of the present invention to provide a coatingcomposition which exhibits not only excellent curability even under lowtemperature conditions, but is also capable of forming a coating havingexcellent mechanical properties, such as impact resistance.

It is a further object of the present invention to provide an adhesiveproperty-imparting composition comprising the above-mentioned blockedpolyisocyanate having excellent compatibility with a plasticizer,wherein the adhesive property-imparting composition, when combined witha plastisol, is capable of imparting excellent low temperature adhesiveproperties to the plastisol.

It is still a further object of the present invention to provide aplastisol composition comprising the above-mentioned adhesiveproperty-imparting composition and a plastisol, wherein the plastisolcomposition is uniform and exhibits low temperature adhesive properties.

The foregoing and other objects, features and advantages of the presentinvention will be apparent from the following detailed description andappended claims.

DETAILED DESCRIPTION OF THE INVENTION

Essentially, in one aspect of the present invention, there is provided ablocked polyisocyanate, which is substantially the same product asobtained by blocking 50 to 100% by mole of the terminal isocyanategroups of a non-blocked polyisocyanate with a thermally dissociativeblocking agent, the non-blocked polyisocyanate being obtained byreacting at least one diisocyanate selected from the group consisting ofan aliphatic diisocyanate and an alicyclic diisocyanate with apolyhydroxy compound having an average number of hydroxyl groups of from4.5 to 10, and removing substantially all unreacted diisocyanatemonomers,

the non-blocked polyisocyanate having the following characteristics (a)to (d):

(a) a cyclic isocyanate trimer content of 10% or less, in terms of aratio of the area of a peak ascribed to a cyclic isocyanate trimer,relative to the total area of all peaks ascribed to the non-blockedpolyisocyanate in a gel permeation chromatogram thereof;

(b) an average number of terminal isocyanate groups of from 5 to 20;

(c) a number average molecular weight of from 1,200 to 10,000 asmeasured by gel permeation chromatography (GPC); and

(d) a terminal isocyanate group content of from 5 to 20% by weight,

the blocked polyisocyanate having the following characteristics (e) to(g):

(e) an average number of blocked terminal isocyanate groups of from 5 to20;

(f) a blocked terminal isocyanate group content of from 2 to 20% byweight; and

(g) a number average molecular weight of from 1,500 to 15,000 asmeasured by GPC.

For an easy understanding of the present invention, the essentialfeatures and various preferred embodiments of the present invention areenumerated below.

1. A blocked polyisocyanate, which is substantially the same product asobtained by blocking 50 to 100% by mole of the terminal isocyanategroups of a non-blocked polyisocyanate with a thermally dissociativeblocking agent, the non-blocked polyisocyanate being obtained byreacting at least one diisocyanate selected from the group consisting ofan aliphatic diisocyanate and an alicyclic diisocyanate with apolyhydroxy compound having an average number of hydroxyl groups of from4.5 to 10, and removing substantially all unreacted diisocyanatemonomers,

the non-blocked polyisocyanate having the following characteristics (a)to (d):

(a) a cyclic isocyanate trimer content of 10% or less, in terms of aratio of the area of a peak ascribed to a cyclic isocyanate trimer,relative to the total area of all peaks ascribed to the non-blockedpolyisocyanate in a gel permeation chromatogram thereof;

(b) an average number of terminal isocyanate groups of from 5 to 20;

(c) a number average molecular weight of from 1,200 to 10,000 asmeasured by gel permeation chromatography (GPC); and

(d) a terminal isocyanate group content of from 5 to 20% by weight,

the blocked polyisocyanate having the following characteristics (e) to(g):

(e) an average number of blocked terminal isocyanate groups of from 5 to20;

(f) a blocked terminal isocyanate group content of from 2 to 20% byweight; and

(g) a number average molecular weight of from 1,500 to 15,000 asmeasured by GPC.

2. The blocked polyisocyanate according to item 1 above, wherein thepolyhydroxy compound is selected from the group consisting of apolyether polyol, a polyester polyol and a mixture thereof.

3. The blocked polyisocyanate according to item 2 above, wherein thepolyhydroxy compound is a polyether polyol to which at least one organicoxide selected from the group consisting of alkylene oxides andphenylalkylene oxides is addition-bonded.

4. The blocked polyisocyanate according to item 3 above, wherein thealkylene oxide is selected from ethylene oxide, propylene oxide,butylene oxide and cyclohexene oxide, and the phenylalkylene oxide isselected from styrene oxide and phenylpropylene oxide.

5. The blocked polyisocyanate according to item 4 above, wherein thepolyhydroxy compound is a polyether polyol to which propylene oxide isaddition-bonded.

6. The blocked polyisocyanate according to item 1 above, which has anallophanate bond in a molecule thereof.

7. The blocked polyisocyanate according to item 1 above, wherein thethermally dissociative blocking agent is selected from the groupconsisting of an alkylphenol compound, an oxime compound, an acid amidecompound, an active methylene compound and a mixture thereof.

8. A coating composition comprising:

(A) a polyol having a hydroxyl value of from 10 to 500 mg KOH/g, an acidvalue of from 0 to 200 mg KOH/g, and a number average molecular weightof from 300 to 60,000; and

(B) a blocked polyisocyanate of any one of items 1 to 7 above.

9. The coating composition according to item 8 above, wherein the polyolis selected from the group consisting of an aliphatic hydrocarbonpolyol, a polyether polyol, a polyester polyol, an epoxy polyol, afluoropolyol, an acrylic polyol and a mixture thereof.

10. An adhesive property-imparting composition comprising a blockedpolyisocyanate of any one of items 1 to 7 above and at least one memberselected from the group consisting of a plasticizer for the blockedpolyisocyanate and a solvent for the blocked polyisocyanate.

11. A plastisol composition comprising a plastisol and an adhesiveproperty-imparting composition of item 10 above.

The present invention is explained below in more detail.

The diisocyanate used in the present invention is at least onediisocyanate selected from the group consisting of an aliphaticdiisocyanate and an alicyclic diisocyanate. As an aliphaticdiisocyanate, a C₄ -C₃₀ aliphatic diisocyanate is preferred, and as analicyclic diisocyanate, a C₈ -C₃₀ alicyclic diisocyanate is preferred.Examples of diisocyanates include tetramethylene-1,4-diisocyanate,pentamethylene-1,5-diisocyanate, hexamethylene diisocyanate,2,2,4-trimethylhexamethylene-1,6-diisocyanate, lysine diisocyanate,isophorone diisocyanate, 1,3-bis(isocyanatomethyl)-cyclohexane and4,4'-dicyclohexylmethane diisocyanate. Among them, hexamethylenediisocyanate (hereinbelow, frequently referred to simply as "HMDI") andisophorone diisocyanate (hereinbelow, frequently referred to simply as"IPDI") are preferred from the viewpoint of commercial availability ofthe diisocyanate, and excellent weatherability of a coating formed froma coating composition as a final product which is produced using thediisocyanate. The above-mentioned diisocyanates can be used individuallyor in combination.

The polyhydroxy compound used in the present invention has an averagenumber of hydroxyl groups of from 4.5 to 10, preferably from 5 to 8. Theterm "average number of hydroxyl groups" means an average number ofhydroxyl groups contained in one molecule of a polyhydroxy compound. Theaverage number of hydroxyl groups can be calculated from the numberaverage molecular weight of the polyhydroxy compound and the weight partof all hydroxyl groups contained in one part by weight of thepolyhydroxy compound (hereinafter, frequently referred to as "hydroxylgroup content"), according to the following formula (1): ##EQU1##

Examples of polyhydroxy compounds include:

1) dipentaerythritol and derivatives thereof;

2) sugar alcohols, such as L-arabinitol, ribitol, xylitol, sorbitol,mannitol, galactitol and rhamnitol;

3) monosaccharides, such as glucose, mannose, galactose, fructose andsorbose;

4) disaccharides, such as trehalose, cane sugar, maltose, cellobiose,gentiobiose, lactose and melibiose;

5) trisaccharides, such as raffinose, gentianose and melezitose; and

6) tetrasaccharides, such as stachyose.

In addition to the above-mentioned polyhydroxy compounds, there can alsobe mentioned polyether polyols, polyester polyols and epoxy polyols,which are obtained from at least one of the above-mentioned polyhydroxycompounds.

Examples of polyether polyols include polyether polyols obtained byaddition-bonding at least one organic oxide selected from the groupconsisting of alkylene oxides (such as ethylene oxide, propylene oxide,butylene oxide and cyclohexene oxide) and phenylalkylene oxides (such asstyrene oxide and phenylpropylene oxide) to at least one of theabove-mentioned polyhydroxy compounds in the presence of a stronglybasic catalyst (such as hydroxides of lithium, sodium and potassium;alcoholates; and alkylamines); polyether polyols obtained by reactingmultifunctional compounds, such as ethylenediamine, with analkyleneoxide; and polymeric polyols obtained by polymerizing acrylamideor the like using the above-mentioned polyethers as reaction media.

Examples of polyester polyols include polyester polyol resins obtainedby a condensation reaction of at least one organic dibasic acid(selected from succinic acid, adipic acid, sebacic acid, dimer acid,maleic anhydride, phthalic anhydride, isophthalic acid and terephthalicacid) with at least one polyhydric alcohol (selected from ethyleneglycol, propylene glycol, diethylene glycol, neopentyl glycol,trimethylolpropane and glycerin); and polycaprolactam polyols, which areobtained by ring-opening, addition polymerization of ε-caprolactam witha polyhydric alcohol.

Examples of epoxy polyols include epoxy polyols of a novolak type, aβ-methylepichlorohydrin type, a cyclic oxirane type, a glycidyl ethertype, a glycol ether type, an epoxidized aliphatic unsaturated compoundtype, an epoxidized fatty acid ester type, a polycarboxylic ester type,an aminoglycidyl type, an epoxidized halogenated compound type, and aresorcin type.

Among the above-mentioned polyols as polyhydroxy compounds used in thepresent invention, polyether polyols and polyester polyols arepreferred. Polyether polyols to which at least one organic oxideselected from the group consisting of alkylene oxides and phenylalkyleneoxides is addition-bonded are more preferred. With respect to alkyleneoxides and phenylalkylene oxides which are to be addition-bonded topolyether polyols, the alkylene oxide is preferably selected fromethylene oxide, propylene oxide, butylene oxide and cyclohexene oxide,and the phenylalkylene oxide is preferably selected from styrene oxideand phenylpropylene oxide. As a polyhydroxy compound used in the presentinvention, polyether polyols to which propylene oxide is addition-bondedare most preferred.

The above-mentioned polyols have the number average molecular weight ofpreferably from 500 to 5,000, more preferably from 600 to 3,000. Theabove-mentioned polyols can be used individually or in combination.Further, the above-mentioned polyols can be urethane-modified prior touse thereof.

For obtaining the non-blocked polyisocyanate to be used in the presentinvention, it is preferred that an aliphatic diisocyanate and/or analicyclic diisocyanate be reacted with a polyhydroxy compound in amanner such that the diisocyanate and the polyhydroxy compound be usedin such amounts that the isocyanate group/hydroxyl group equivalentratio is in the range of from 2/1 to 30/1. When the isocyanategroup/hydroxyl group equivalent ratio is less than 2/1, the viscosity ofthe reaction mixture obtained by the above reaction becomes too high, sothat it is difficult to conduct a commercial-scale production of thenon-blocked polyiso-cyanate. When the isocyanate group/hydroxyl groupequivalent ratio is more than 30/1, the productivity of the non-blockedpolyisocyanate becomes low. For efficiently obtaining the non-blockedpolyisocyanate, it is more preferred that a diisocyanate and apolyhydroxy compound be used in such amounts that the isocyanategroup/hydroxyl group equivalent ratio is in the range of from 5/1 to20/1. A diisocyanate can be mixed with a polyhydroxy compound prior tothe heating of the reaction system to a reaction temperature (describedbelow). Alternatively, a diisocyanate alone can be charged in a reactorand heated to the reaction temperature and then, to the heateddiisocyanate can be added a polyhydroxy compound batchwise orportionwise.

The above-mentioned reaction may be conducted in the presence of asolvent. When using a solvent, it is necessary that the solvent be inertto isocyanate groups.

The reaction temperature of the reaction between the diisocyanate andthe polyhydroxy compound is generally from 60° C. to 200° C., preferablyfrom 130° C. to 180° C. When the reaction temperature is lower than 60°C., the reaction rate becomes low, so that the increase in the averagenumber of terminal isocyanate groups in the produced polyisocyanate(this increase is presumed to be due to an allophanation reaction)becomes slow. When the reaction temperature is higher than 200° C., aproblem arises such that the produced polyisocyanate suffersdiscoloration.

The reaction time may vary depending on the reaction temperature. Thereaction time is generally from 1 to 8 hours, preferably from 2 to 6hours.

The reaction may be conducted in the presence of a catalyst. When usinga catalyst, a basic catalyst is preferred. Examples of basic catalystsinclude:

1) quaternary ammonium compounds, such as a hydroxide of atetraalkylammonium, and a tetraalkyl ammonium salt of an organic weakacid, such as acetic acid or capric acid;

2) tertiary amine compounds, such as trioctylamine,1,4-diazabicyclo[2.2.2]octane, 1,8-diazabicyclo[5.4.0]-7-undecene and1,5-diazabicyclo[4.3.0]-5-nonene; and

3) compounds which are known to promote an allophanation reaction, suchas an acetylacetonato complex with a metal (e.g., zinc), and a metalsalt of an organic weak acid (e.g., zinc, tin, lead or iron). Thecatalyst is used generally in an amount of from 0.001% to 1.0%, based onthe amount of the diisocyanate.

By the above-mentioned reaction of a diisocyanate and a polyhydroxycompound, a polyisocyanate having urethane bonds is produced. In thisreaction, at least a part of the urethane bonds present in thepolyisocyanate may be converted into allophanate bonds. The conversionratio of urethane bonds into allophanate bonds is generally 10% or more,preferably 20% or more. When the conversion ratio is less than 10%, theviscosity of the produced polyisocyanate becomes unfavorably too high.

In the present invention, a non-blocked polyisocyanate having a largeaverage number of terminal isocyanate groups is obtained by theconversion of the urethane bonds to the allophanate bonds. From such anon-blocked polyisocyanate, the blocked polyisocyanate of the presentinvention can be obtained. By using the obtained blocked polyisocyanate,a coating composition comprising the blocked polyisocyanate of thepresent invention as a curing agent and a polyol as a main agent can beobtained, wherein the coating composition has not only excellentcurability even under low temperature conditions, but is also capable offorming a coating having excellent impact resistance. Further, anadhesive property-imparting composition containing the blockedpolyisocyanate of the present invention can be obtained. The adhesiveproperty-imparting composition can be combined with a plastisol forproviding a plastisol composition having excellent adhesive propertieseven under low temperature conditions.

In the above-mentioned reaction of a diisocyanate with a polyhydroxycompound, a polyisocyanate is produced in a yield of from 20 to 70% byweight. In the present invention, the yield of polyisocyanate is definedby the following formula: ##EQU2## wherein α represents the total amountof diisocyanate monomers and a polyhydroxy compound, and β representsthe amount of unreacted diisocyanate monomers which are removed aftercompletion of the reaction.

After completion of the reaction, substantially all unreacteddiisocyanate monomers are removed from the resultant reaction mixture tothereby obtain a non-blocked polyisocyanate, which is to be subsequentlysubjected to a blocking reaction.

In the present invention, the term "average number of terminalisocyanate groups of a non-blocked polyisocyanate" means an averagenumber of isocyanate groups per molecule of a non-blockedpolyisocyanate, and can be calculated by the following formula (2):##EQU3## wherein the terminal isocyanate group concentration is definedas a weight ratio of terminal isocyanate groups of the non-blockedpolyisocyanate to the non-blocked polyisocyanate.

In the present invention, the non-blocked polyisocyanate has an averagenumber of terminal isocyanate groups of from 5 to 20, preferably from 5to 14. When a non-blocked polyisocyanate having an average number ofterminal isocyanate groups of less than 5 is used to prepare a blockedpolyisocyanate, a coating composition produced by using such a blockedpolyisocyanate is likely to have unsatisfactory curing properties. Onthe other hand, when a non-blocked polyisocyanate having an averagenumber of terminal isocyanate groups of more than 20 is used to preparea blocked polyisocyanate, a coating composition produced by using such ablocked polyisocyanate cannot be suitably used for providing a coatinghaving good appearance, such as smooth surface finish.

The terminal isocyanate group content of the non-blocked polyisocyanateused for producing the blocked polyisocyanate of the present inventionis from 5 to 20% by weight. When a non-blocked polyisocyanate having aterminal isocyanate group content of less than 5% by weight is used toprepare a blocked polyisocyanate, a satisfactory crosslink densitycannot be obtained with respect to a coating obtained by curing thecoating composition containing the blocked polyisocyanate of the presentinvention as a curing agent and containing a polyol as a main agent. Onthe other hand, when a non-blocked polyisocyanate having a terminalisocyanate group content of more than 20% by weight is used to prepare ablocked polyisocyanate, the crosslink density tends to become too high.

The non-blocked polyisocyanate used for producing the blockedpolyisocyanate of the present invention has a number average molecularweight of from 1,200 to 10,000 as measured by gel permeationchromatography. When a non-blocked polyisocyanate having a numberaverage molecular weight of less than 1,200 is used to prepare a blockedpolyisocyanate, the crosslink density becomes too high with respect to acoating obtained by curing the coating composition containing theblocked polyisocyanate of the present invention as a curing agent andcontaining a polyol as a main agent. On the other hand, when anon-blocked polyisocyanate having a number average molecular weight ofmore than 10,000 is used to prepare a blocked polyisocyanate, a coatingobtained by curing a coating composition containing such a blockedpolyisocyanate has poor appearance, such as low surface smoothness.

The viscosity of the non-blocked polyisocyanate is from 2,000 to 200,000mPa·s/25° C., preferably from 5,000 to 100,000 mPa·s/25° C. When anon-blocked polyisocyanate having a viscosity of less than 2,000mPa·s/25° C. is used to prepare a blocked polyisocyanate, a coatingcomposition containing such a blocked polyisocyanate suffers sags whencoated on a vertical surface. When a non-blocked polyisocyanate having aviscosity of more than 200,000 mPa·s/25° C. is used to prepare a blockedpolyisocyanate, a coating composition containing such a blockedpolyisocyanate has poor fluidity, so that a coating obtained from thecoating composition has poor appearance, such as low surface smoothness.

In Unexamined Japanese Patent Application Laid-Open Specification No.6-293878 (corresponding to International Patent Application PublicationNo. WO 94/18254), the present inventors previously proposed a urethanecoating composition containing a blocked polyisocyanate obtained from apolyisocyanate having an isocyanurate structure having an average numberof terminal isocyanate groups of from 4.5 to 10. However, the blockedpolyisocyanate of the present invention having a limited content ofcyclic isocyanate trimer is different in structure from theabove-mentioned blocked polyisocyanate which was previously proposed inUnexamined Japanese Patent Application Laid-Open Specification No.6-293878. The coating composition of the present invention is acomposition containing such a blocked polyisocyanate of the presentinvention.

In the non-blocked polyisocyanate used for producing the blockedpolyisocyanate of the present invention, the cyclic isocyanate trimercontent is 10% or less. When a non-blocked polyisocyanate having acyclic isocyanate trimer content of more than 10% is used to prepare ablocked polyisocyanate, the low temperature curability of a coatingcomposition containing such a blocked polyisocyanate is poor. In thepresent invention, the cyclic isocyanate trimer content of thenon-blocked polyisocyanate is expressed in terms of a ratio of the areaof a peak ascribed to a cyclic isocyanate trimer, relative to the totalarea of all peaks ascribed to the non-blocked polyisocyanate in a gelpermeation chromatogram thereof, wherein the gel permeationchromatography is performed by using a refractometer as the detector andusing tetrahydrofuran as the carrier.

Examples of thermally dissociative blocking agents used for blocking theterminal isocyanate groups of a non-blocked polyisocyanate includealcohol compounds, alkylphenol compounds, phenol compounds, activemethylene compounds, mercaptan compounds, acid amide compounds, acidimide compounds, imidazole compounds, urea compounds, oxime compounds,amine compounds, imide compounds, and pyrazole compounds. More specificexamples of thermally dissociative blocking agents are described initems (1) to (14) below.

(1) Alcohol compounds: methanol, ethanol, 2-propanol, n-butanol,sec-butanol, 2-ethyl-1-hexanol, 2-methoxyethanol, 2-ethoxyethanol,2-butoxyethanol and the like.

(2) Alkylphenol compounds: monoalkylphenols and dialkylphenols bothsubstituted with an alkyl group having 4 or more carbon atoms, such aspara-, orthoand metha-isomers of n-propylphenol, i-propylphenol,nbutylphenol, sec-butylphenol, t-butylphenol, n-hexylphenol,2-ethylhexylphenol, n-octylphenol, n-nonylphenol, dodecylphenol,octadecyl phenol and the like; and 2,4- and 2,6-isomers ofdi-n-propylphenol, diisopropylphenol, isopropylcresol, di-n-butylphenol,di-t-butylphenol, di-sec-butylphenol, diamylphenol, di-noctylphenol,di-2-ethylhexylphenol, di-n-nonylphenol and the like.

(3) Phenol compounds: phenol, cresol, ethylphenol, styrenated phenol,hydroxybenzoic ester and the like.

(4) Active methylene compounds: dimethyl malonate, diethyl malonate,methyl acetoacetate, ethyl acetoacetate, acetyl acetone and the like.

(5) Mercaptan compounds: butylmercaptan, dodecylmercaptan and the like.

(6) Acid amide compounds: acetanilide, amide acetate, ε-caprolactam,δ-valerolactam, γ-butyrolactam and the like.

(7) Acid imide compounds: succinimide, maleimide and the like.

(8) Imidazole compounds: imidazole, 2-methylimidazole and the like.

(9) Urea compounds: urea, thiourea, ethyleneurea and the like.

(10) Oxime compounds: formaldoxime, acetoaldoxime, acetoxime,methylethylketoxime, cyclohexanone oxime and the like.

(11) Amine compounds: diphenylamine, aniline, carbazole,di-n-propylamine, diisopropylamine, isopropylamine and the like.

(12) Imine compounds: ethyleneimine, polyethyleneimine and the like.

(13) Bisulfites: sodium bisulfite and the like. (14) Pyrazole compounds:pyrazole, 3-methylpyrazole, 3,5-dimethylpyrazole and the like.

Of the above-mentioned thermally dissociative blocking agents, at leastone compound selected from alkylphenol compounds, oxime compounds, acidamide compounds and active methylene compounds is preferred. Especiallypreferred are p-nonylphenol, a para-isomer and ortho-isomer oft-butylphenol, p-dodecylphenol, acetoxime, methylethylketoxime,ε-caprolactam, alkyl actoacetate, and dialkyl malonate. These thermallydissociative blocking agents can be used individually or in combination.For example, a combination of an oxime compound and an active methylenecompound, or a combination of two different types of active methylenecompounds can be used.

By using the above-mentioned thermally dissociative blocking agent, 50to 100% by mole, preferably 80 to 100% by mole of the terminalisocyanate groups of the non-blocked polyisocyanate are blocked. Whenthe amount of the blocked terminal isocyanate groups is less than 50% bymole, a coating composition containing such a blocked polyisocyanate anda polyol has poor storage stability.

In the blocking reaction between the non-blocked polyisocyanate and thethermally dissociative blocking agent, a solvent may be used if desired.When a solvent is used, the solvent must be inert to an isocyanategroup.

In the blocking reaction between the non-blocked polyisocyanate and thethermally dissociative blocking agent, a catalyst may be used. As thecatalyst, an organic acid salt of a metal, such as tin, zinc or lead, atertiary amine compound, and an alcoholate of an alkali metal, such assodium, can be used.

The blocking reaction is generally conducted at a temperature of from-20 to 150° C., preferably from 30 to 100° C. When the reactiontemperature is higher than 150° C., side reactions are likely to occur.On the other hand, when the reaction temperature is lower than -20° C.,the reaction rate is too low.

The blocked polyisocyanate of the present invention thus obtained hasthe following characteristics (e) to (g):

(e) an average number of blocked terminal isocyanate groups of from 5 to20;

(f) a blocked terminal isocyanate group content of from 2 to 20% byweight; and

(g) a number average molecular weight of from 1,500 to 15,000 asmeasured by GPC.

The above-mentioned blocked polyisocyanate having such a large averagenumber of blocked terminal isocyanate groups as mentioned above does notcause a curing reaction at room temperature but is capable of causing acuring reaction even at a temperature in the range of from 100 to 130°C. (such a temperature is low as compared to the temperature at whichthe conventional coating compositions can be cured) which is frequentlydesirable from a practical point of view, and functions as an effectivecuring agent for a polyol under such low temperature conditions. Aone-pack type urethane coating composition comprising a polyol as a mainagent and the above-mentioned blocked polyisocyanate not only exhibitsexcellent curability even under low temperature conditions, which cannotbe achieved by the conventional one-pack type urethane coatingcomposition, but is also capable of forming a coating which hasexcellent mechanical properties, such as excellent impact resistance.

In the present invention, the term "average number of blocked terminalisocyanate groups of a blocked polyisocyanate" means an average numberof blocked terminal isocyanate groups per molecule of a blockedpolyisocyanate, and can be calculated by the following formula (3):##EQU4## wherein the blocked terminal isocyanate group concentration isdefined as a weight ratio of all terminal isocyanate groups (inclusiveof the blocked terminal isocyanate groups) of the blocked polyisocyanateto the blocked polyisocyanate.

Examples of polyols used in the coating composition of the presentinvention include an aliphatic hydrocarbon polyol, a polyether polyol, apolyester polyol, an epoxy polyol, a fluoropolyol and an acrylic polyol.

Specific examples of aliphatic hydrocarbon polyols include apolybutadiene having terminal hydroxyl groups and a hydrogenationproduct thereof. Examples of polyether polyols include a polyetherpolyol obtained by subjecting at least one alkylene oxide (such asethylene oxide or propylene oxide) to an addition reaction with at leastone polyhydric alcohol (such as glycerin or propylene glycol) or with atleast one polyfunctional compound (such as ethylenediamine orethanolamine); a polytetramethylene glycol; and a so-called polymerpolyol obtained by polymerizing an acrylamide or the like, using theabove-mentioned polyether polyol as a reaction medium.

Specific examples of polyester polyols include a polyester polyol resinobtainable by condensation polymerization of at least one dibasic acidselected from the group consisting of succinic acid, adipic acid,sebacic acid, dimeric acid, maleic anhydride, phtahalic anhydride,isophthalic acid and terephthalic acid with at least one polyhydricalcohol (such as ethylene glycol, propylene glycol, diethylene glycol,neopentyl glycol, trimethylolpropane and glycerin); and apolycaprolactone obtainable by a ring-opening polymerization ofε-caprolactone with a polyhydric alcohol.

Specific examples of epoxy polyols include compounds of a novolak type,a β-methylepichlorohydrin type, a cyclic oxirane type, a glycidyl ethertype, a glycol ether type, an epoxidized aliphatic unsaturated compoundtype, an epoxidized fatty acid ester type, a polycarboxylic ester type,an aminoglycidyl type, an epoxidized halogenated compound type and aresorcin type; and compounds obtained by modification of theabove-mentioned epoxy polyols with an amino compound, a polyamidecompound or the like.

Specific examples of fluoropolyols include copolymers of fluoroolefinmonomers with at least one comonomer, such as a cyclohexylvinyl ether, ahydroxyalkylvinyl ether and vinyl esters of monocarboxylic acids [suchcopolymers are disclosed in, for example, Unexamined Japanese PatentApplication Laid-Open Specification No. 57-34107 (corresponding to GBPatent No. 2081727) and Unexamined Japanese Patent Application Laid-OpenSpecification No. 61-275311 (corresponding to U.S. Pat. No. 4,640,966).

Specific examples of acrylic polyols include compounds obtainable bycopolymerizing at least one acrylic monomer (having, in a moleculethereof, at least one active hydrogen) with at least one comonomercopolymerizable with the acrylic monomer. Specific examples of acrylicmonomers (having, in a molecule thereof, at least one active hydrogen)include acrylic esters having at least one active hydrogen, such as2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate and 2-hydroxybutylacrylate; methacrylic esters having at least one active hydrogen, suchas 2-hydroxydiethyl methacrylate, 2-hydroxypropyl methacrylate and2-hydroxybutyl methacrylate; and (meth)acrylic esters having two or moreactive hydrogens, such as an acrylic monoester or a methacrylicmonoester of glycerin and an acrylic monoester or a methacylic monoesterof trimethylolpropane. Examples of comonomers copolymerizable with theabove-mentioned acrylic monomers include acrylic acid esters, such asmethyl acrylate, ethyl acrylate, isopropyl acrylate, n-butyl acrylateand 2-ethylhexyl acrylate; methacrylic acid esters, such as methylmethacrylate, ethyl methacrylate, isopropyl methacrylate, n-butylmethacrylate, isobutyl methacrylate, n-hexyl methacrylate, cyclohexylmethacrylate, lauryl methacrylate and glycidyl methacrylate; and one ormore of other polymerizable comonomers, for example, unsaturatedcarboxylic acids (such as acrylic acid, methacrylic acid, maleic acidand itaconic acid), unsaturated amides (such as acrylamide,N-methylolacrylamide and diacetoneacrylamide), styrene, vinyltoluene,vinyl acetate, and acrylonitrile.

It is also possible to use an acrylic polyol obtainable bycopolymerizing the above-mentioned at least one acrylic monomer (having,in a molecule thereof, at least one active hydrogen) with at least onepolymerizable ultraviolet-stable monomer as exemplified in, for example,Unexamined Japanese Patent Application Laid-Open Specification No.1-261409 (corresponding to U.S. Pat. No. 5,239,028) and UnexaminedJapanese Patent Application Laid-Open Specification No. 3-6273.

Polyols used in the present invention have a hydroxyl value of from 10to 500 mg KOH/g, an acid value of from 0 to 200 mg KOH/g, and a numberaverage molecular weight of from 300 to 60,000. Most preferred examplesof polyols are an acrylic polyol, a polyester polyol and an epoxypolyol.

When the hydroxyl value of the polyol is less than 10 mg KOH/g, acoating obtained by curing the coating composition has a low crosslinkdegree and hence does not have desired mechanical properties. When thehydroxyl value exceeds 500 mg KOH/g, a coating obtained by curing thecoating composition has unfavorably low flexibility. When the numberaverage molecular weight is outside the above-mentioned range, it ispossible that a good coating cannot be obtained.

It is preferred that the acid value of the polyol be low, namely notmore than 20 mg KOH/g.

In the coating composition of the present invention, the equivalentratio of the blocked isocyanate groups in the blocked polyisocyanate tothe hydroxyl groups in the polyol is selected in accordance with thedesired properties of the coating, but is usually in the range of from10:1 to 1:10.

Melamine resins may be used in the coating composition of the presentinvention. Examples of melamine resins includehexamethoxymethylolmelamine, a methylol type alkyl melamine, acompletely alkylated type melamine and an imino type melamine. Specificexamples of these melamines include methylated and butylated melamineand butylated melamine. By using these melamine resins, the mechanicalproperties of the coating, such as a hardness thereof, can becontrolled.

Various types of solvents and additives may be optionally used dependingon the uses and purposes. Examples of solvents include hydrocarbons(such as benzene, toluene, xylene, cyclohexane, mineral spirit, naphthaand the like); ketones (such as acetone, methyl ethyl ketone, methylisobutyl ketone and the like); esters (such as ethyl acetate, n-butylacetate, cellosolve acetate and the like); and alcohols (such asn-butanol, isopropyl alcohol and the like). These solvents may be usedindividually or in combination.

Further, if desired, there may also be used curing accelerators (forexample, at least one salt of a carboxylic acid with a metal, such astin, zinc, lead or the like); antioxidants (such as hindered phenols andthe like); UV absorbents (such as benzotriazole, benzophenone and thelike); pigments (such as titanium oxide, carbon black, indigo,quinacridone, pearl mica and the like); metallic powder pigments (suchas aluminum powder and the like); and rheology controlling agents (suchas hydroxyethyl cellulose, urea compounds and the like). These curingaccelerators, antioxidants and the like can be used in amountsconventionally used in the art.

The coating composition thus prepared is useful as materials forundercoating, top coating and intercoating metallic substances (such asa steel plate and a surface-treated steel plate) and plastic substances;a coating material for a precoated metal or a rust-resistant steelplate; and a coating material for imparting fine appearance,weathrability, acid resistance, rust resistance, mechanical strength(such as chipping resistance and impact resistance) and the like toautomobiles. The application of the coating composition onto varioussubstrates can be performed by, for example, roll coating, curtain flowcoating, spray coating, dip coating, electrodeposition coating and thelike.

The blocked polyisocyanate of the present invention has also anexcellent performance as an adhesive property-imparting agent.Specifically, by diluting the blocked polyisocyanate of the presentinvention with a plasticizer therefor and/or a solvent therefor, anadhesive property-imparting composition can be obtained. The dilutionwith a plasticizer and/or a solvent is carried out for the purposes oflowering the viscosity of the adhesive property-imparting compositionand improving the processability thereof and the like. Further, when theadhesive property-imparting composition is combined with a plastisol(explained below) and the resultant plastisol composition is subjectedto curing, the plasticizer used for the dilution acts as one componentof the cured plastisol composition and exhibits an effect for impartinga desired mechanical properties to the cured plastisol composition. Onthe other hand, when the adhesive property-imparting composition isadded to a plastisol, the solvent used for the dilution improves theprocessability of the plastisol composition, but evaporates later anddoes not remain in a cured plastisol composition.

The concentration of the plasticizer and/or the solvent in the adhesiveproperty-imparting composition varies depending on uses and purposes,but is usually from 20 to 80% by weight.

With respect to the plasticizer, there is no particular limitation aslong as it is a plasticizer usually used for vinyl chloride polymers.Examples of plasticizers include phthalic esters and isophthalic esters,such as dimethyl phthalate, diethyl phthalate, di-n-butyl phthalate,diheptyl phthalate, di-n-octyl phthalate, di-2-ethylhexyl phthalate(hereinafter referred as "DOP"), diisononyl phthalate, octyl decylphthalate, diisodecyl phthalate, butyl benzyl phthalate, di-2-ethylhexylisophthalate and the like; aliphatic esters, such as di-2-ethylhexyladipate, di-n-decyl adipate, diisodecyl adipate, di-2-ethylhexylazelate, dibutyl sebacate, di-2-ethylhexyl sebacate and the like;phosphoric esters, such as tributyl phosphate, tri-2-ethylhexylphosphate, 2-ethylhexyl diphenyl phosphate, tricresyl phosphate and thelike; epoxides, such as epoxidized soybean oil, epoxidized tall oilfatty acid 2-ethylhexyl ester and the like. Of them, preferred arephthalic esters, and more preferred are di-n-octyl phthalate, DOP,diisononyl phthalate and octyl decyl phthalate. These plasticizers canbe used individually or in combination.

The solvent can be appropriately selected from hydrocarbons, such asbenzene, toluene, xylene, cyclohexane, mineral spirit, naphtha and thelike; ketones, such as acetone, methyl ethyl ketone, methyl isobutylketone and the like; esters, such as ethyl acetate, n-butyl acetate,cellosolve acetate and the like; and alcohols, such as n-butanol,isopropyl alcohol and the like. These solvents can be used individuallyor in combination.

Further, plasticizers and solvents can be used in combination.

If desired, conventionally known adhesive property-imparting agents, forexample, polyamide amine compounds (obtained by reacting a polymericfatty acid, such as a dimer acid, with a polyamine compound) andaliphatic polyamines, (such as ethylene diamine, diethylene triamine)may also be used in combination with solvents and/or plasticizers.

The adhesive property-imparting composition is usually used forimproving the low temperature adhesion properties of a plastisol (whichis a dispersion of a vinyl chloride polymer in the above-mentionedplasticizers). The amount of the adhesive property-imparting compositionto be added to the plastisol varies depending on the use of theplastisol composition. However, the amount of the adhesiveproperty-imparting composition to be added is usually from 0.5 to 15% byweight, based on the weight of the vinyl chloride polymer in theplastisol. Conventional blocked polyisocyanates, especially conventionalblocked polyisocyanates derived from an aliphatic diisocyanate and/or analicylic diisocyanate, have poor compatibility with the above-mentionedplasticizers, so that a conventional plastisol composition containing aconventional blocked polyisocyanate and a plasticizer has poor adhesionproperties at low baking temperatures. Therefore, the use of theconventional plastisol composition is limited. By contrast, the blockedpolyisocyanate of the present invention has good compatibility with theabove-mentioned plasticizers (despite the fact that the blockedpolyisocyanate of the present invention is derived from an aliphaticdiisocyanate and/or an alicyclic diisocyanate), so that the blockedpolyisocyanate of the present invention has the ability to impartexcellent adhesion properties to a plastisol even at low bakingtemperatures.

The above-mentioned vinyl chloride polymer used in the plastisolcomprises a base resin having a particle diameter of 5 μm or less,preferably from 0.05 to 3 μm, and a paste resin, and optionally ablending resin which is usually employed together with a paste resin.The above-mentioned base resin is obtained by subjecting vinyl chlorideor a mixture of vinyl chloride and a comonomer copolymerizable withvinyl chloride to emulsion polymerization in the presence of anemulsifier and an aqueous polymerization initiator. The above-mentionedpaste resin is obtained by a microsuspension polymerization method inwhich vinyl chloride or a mixture of vinyl chloride and a comonomercopolymerizable with vinyl chloride is mechanically dispersed (at leastpartially micro-dispersed) in the presence of a dispersant and anoil-soluble polymerization initiator and then, subjected to suspensionpolymerization. Further, a polyvinyl chloride resin and/or a vinylchloride copolymer resin which is obtained by ordinary suspensionpolymerization and has a relatively large particle diameter may be addedto the above-mentioned vinyl chloride polymer, as long as the viscosity,flowability and processability of the plastisol composition is notadversely affected. Examples of comonomers copolymerizable with vinylchrolide used for producing a vinyl chloride copolymer include vinylesters, such as vinyl acetate, vinyl propionate and vinyl laurate;acrylic esters, such as methyl acrylate, ethyl actylate, butyl acrylate,2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate and 3-hydroxybutylacrylate; methacrylic esters, such as methyl methyacrylate, ethylmethacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylateand 3-chloro-2-hydroxypropyl methacrylate; maleic esters, such asdibutyl maleate, diethyl maleate and ethyl 2-hydroxyethyl maleate;fumaric esters, such as dibutyl fumarate and diethyl fumarate; vinylethers, such as vinyl methyl ether, vinyl butyl ether and vinylhydroxybutyl ether, vinyl octyl ether; vinyl cyanides, such asacrylonitrile and methacrylonitrile; α-olefins, such as ethylene,propylene and styrene; vinylidene halides or vinyl halides other thanvinyl chloride, such as vinylidene chloride and vinyl bromide; andn-methylol acrylamide.

In addition to the above-mentioned components, the plastisol compositionmay further contain additives, such as an agent for accelerating thedissociation of blocking groups from the terminal isocyanate groups ofthe blocked polyisocyanate, a diluent, a filler, a thickening agent, acolorant and the like. Examples of agents for accelerating thedissociation of blocking groups from the terminal isocyanate groupsinclude salts of a carboxylic acid with a metal, such as tin, zinc orlead; and a tin oxide, a zinc oxide and a lead oxide. The agent foraccelerating the dissociation of blocking groups from the terminalisocyanate groups is used in an amount of from 0 to 10% by weight, basedon the weight of the plastisol. Examples of diluents include aliphatichydrocarbon solvents (such as hexane, heptane, octane, nonane anddecane), naphthene type hydrocarbon solvents (such as cyclohexane,methyl cyclohexane, dimetyl cyclohexane and diethylcyclohexane), andaromatic hydrocarbon solvents [such as toluene, xylene, ethyl benzeneand, Solvesso # 100 and Solvesso # 150 (both of which are manufacturedand sold by Exxon, U.S.A.]. The diluent is used for the purpose ofcontrolling the viscosity or the like of the plastisol composition. Thediluent is used in an amount of from 0 to 10% by weight, based on theweight of the plastisol. Examples of fillers include inorganic fillers,such as light calcium carbonate, heavy calcium carbonate, talc,diatomite, kaolin and barium sulfate; and organic fillers, such as acellulose powder, a powdery rubber and a regenerated rubber. The filleris used for the purposes of maintaining the mechanical properties (suchas hardness) of a gelation product of the plastisol composition and alsopreventing the plastisol composition from sagging at the time of thecoating operation. The filler can be used in an amount of from 50 to300% by weight, based on the weight of the plastisol. Examples ofthickening agents include anhydrous silica, organic bentonite and ametallic soap and the like. The thickening agent is used for the purposeof, for example, controlling the viscosity of the plastisol composition.The thickening agent is used in amount of from 0 to 50% by weight, basedon the weight of the plastisol.

The coating weight of the plastisol composition thus prepared is usuallyfrom 150 to 3,000 g/m². The thickness of the coating is usually from0.15 to 3 mm. After the coating operation, the baking of the coating isconducted. The baking of the coating can be conducted even at atemperature as low as from 110° C. to 130° C., which is frequentlydesirable from a practical point of view. The baking time is usuallyfrom 20 to 40 minutes.

Examples of coating methods for the plastisol composition of the presentinvention include spraying, brushing, dipping, injection, pouring,air-spraying and the like.

The plastisol composition of the present invention has a wide variety ofindustrial applications. For example, the plastisol composition of thepresent invention can be used not only as a sealant, an undercoatingmaterial and an anti-chipping agent, but also in the production of PCM(precoated metal), such as vinyl chloride polymer-coated steel plates.The plastisol composition of the present invention can be advantageouslyused especially in automobile industry, for example, as an undercoatingmaterial for a polyester resin coating composition, an epoxy resincoating composition, an acrylic resin coating composition or the like.Specifically, the plastisol composition of the present invention can beadvantageously applied onto automobile bodies having a coating formedthereon by cationic electrodeposition, wherein the plastisol compositionis employed for the purposes of preventing rust and providing acushioning effect against pebbles or the like hitting the car body.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinbelow, the present invention will be described in more detail withreference to the following Reference Examples, Comparative ReferenceExamples, Examples and Comparative Examples, but they should not beconstrued as limiting the scope of the present invention.

In the following Examples and Comparative Examples, various propertieswere measured and/or evaluated by the following methods.

(1) Number Average Molecular Weight:

A sample of polyisocyanate for measurement of the number averagemolecular weight thereof was prepared by dissolving the polyisocyanateto tetrahydrofuran (THF) so that the final concentration of thepolyisocyanate in THF became about 0.25% by weight. The prepared samplewas subjected to gel permeation chromatography (GPC) using HLC-802A(manufactured and sold by TOSOH Corporation, Japan) to thereby determinethe number average molecular weight thereof by using a calibration curveobtained with respect to a standard polystyrene. When the number averagemolecular weight was less than 2,000, the GPC was conducted usingcolumns G1000HXL, G2000HXL and G3000HXL (each of which was manufacturedand sold by TOSOH Corporation, Japan), and using THF as a carrier,wherein a refractive index detector and a chromatoprocessor (CP-8000,manufactured and sold by TOSOH Corporation, Japan) were used. When thenumber average molecular weight was 2,000 or more, the GPC was conductedusing columns G2000HXL, G4000HXL and G5000HXL (each of which wasmanufactured and sold by TOSOH Corporation, Japan), and using THF as acarrier, wherein a refractive index detector and a chromatoprocessor(CP-8000, manufactured and sold by TOSOH Corporation, Japan) were used.

(2) Cyclic Isocyanate Trimer Content:

A cyclic isocyanate trimer content was expressed in terms of a ratio ofthe area of a peak ascribed to a cyclic isocyanate trimer [for example,in the case of a trimer derived from hexamethylene diisocyanate (HMDI),the area of a peak corresponding to the molecular weight 504 of thecyclic isocyanate trimer derived from HMDI], relative to the total areaof all peaks ascribed to the non-blocked polyisocyanate in a gelpermeation chromatogram.

(3) Allophanate Bond Concentration:

The allophanate bond concentration of a polyisocyanate composition wasmeasured and evaluated by the following method.

About 0.5 g of acetone-d₆ [(CD₃)₂ CO], 2 to 5 mg of a samplepolyisocanate and about 100 ppm by volume, based on the volume of theacetone-d₆ [(CD₃)₂ CO] of tetramethylsilane were mixed in a sample tubeto prepare a sample. The prepared sample was analyzed by ¹ H-NMR usingFT-NMR (FX90Q, sold and manufactured by JEOL Ltd., Japan). Using theintegral (area) of a peak corresponding to the allophanate bond ([A])and the integral (area) of a peak corresponding to the urethane bond([U]) obtained from the above analysis, the allophanate bondconcentration (%) was calculated using the following formula: ##EQU5##

The allophanate bond concentrations were classified into three degreesof A, B and C in accordance with the following criteria:

    ______________________________________                                        Concentration   Criteria                                                      ______________________________________                                        90% or more     A                                                               10% or more and B                                                             less than 90%                                                                 less than 10%  C.                                                           ______________________________________                                    

(4) Viscosity of Polyisocyanate:

The viscosity of polyisocyanate was measured using an Emila-typerotating viscometer (manufactured and sold by Reciprotor Co., Denmark).

A sample of polyisocyanate was placed in a sample holder maintained at25° C. The rotor of the viscometer was rotated until the viscosityindicated by the viscometer became constant. The value of this constantviscosity was taken as the viscosity of the measured polyisocyanate.

(5) Gel Ratio of Coating Composition:

The gel ratio of a coating composition was determined as follows.

0.1 g of the coating was subjected to extraction with 50 g of acetone at20° C. for 24 hours. The gel ratio was calculated using the followingformula:

    Gel Ratio(%)=(the weight of coating remaining undissolved after immersion of the coating in acetone for 24 hours/the original weight of the coating)×100.

The gel ratio was evaluated in accordance with the following criteria:

    ______________________________________                                               Gel ratio                                                                              Criteria                                                      ______________________________________                                               90% or more                                                                            ⊚                                                80% to ∘                                                          less than 90%                                                                 less than 80%  x.                                                           ______________________________________                                    

When an epoxy polyol was used as a main agent of a coating composition,methanol was used instead of the acetone in the above-mentionedextraction step.

(6) Impact Resistance Property:

The evaluation of the impact resistance of a coating composition wasconducted by using Du-pont impact tester. A steel plate having a coatingprepared from a coating composition was placed on a flat bearer. Afterdisposing a center of impact (radius: 1/3 inch) thereon, a load of 500 gwas caused to fall on the center of impact from the height of 50 cm. Thecoating at -20° C. was observed. The impact resistance of the coatingwas evaluated in accordance to the following criteria:

    ______________________________________                                        Impact resistance                                                                              Criteria                                                     ______________________________________                                        no damage observed                                                                             ∘                                                  on the coating                                                                damage observed  x.                                                           on the coating                                                              ______________________________________                                    

(7) Adhesive Property:

The adhesive property of a plastisol composition was measured andevaluated by the following method.

A plastisol composition was applied onto a first adherend (a steel platehaving a coating formed by cationic eltrodeposition) at a thickness of0.5 mm, and a second adherend (which is the same as the first adherend)was placed on plastisol-coated face of the first adherend, followed byba king at 120° C. for 30 minutes. The shearing adhesion strength(kg/cm²) was measured at a pulling rate of 5 mm/hr. The shearingadhesion strength was evaluated in accordance with the followingcriteria:

    ______________________________________                                        Shearing adhesion strength                                                                       Criteria                                                   ______________________________________                                        15 kg/cm.sup.2 or more                                                                           ∘                                                less than 15 kg/cm.sup.2  x.                                                ______________________________________                                    

(8) Content of Non-Blocked Isocyanate Groups:

The content (% by weight) of non-blocked isocyanate groups in anon-blocked polyisocyanate was determined as follows.

About 2 to 5 g of a polyisocyanate was accurately weighed and taken as asample. 20 ml of toluene and 20 ml of a 2N solution of n-dibutylamine intoluene were added to the sample polyisocyanate. The resultant wasallowed to stand at room temperature for 15 minutes, and then subjectedto back titration using 1N hydrochloric acid. Using Bromocresol Green asan indicator, the content of non-blocked isocyanate groups wasdetermined in accordance with the following formula:

    The content (% by weight) of non-blocked isocyanate groups={(titer of blank titration)-(titer of sample titration)}×42/{weight (g) of sample×1000}×100.

The titer of blank titration means a titer obtained by conductingtitration in substantially the same manner as mentioned above, exceptthat the polyisocyanate was not used.

(9) Content of Blocked Isocyanate Groups:

The blocked isocyanate group content of the blocked polyisocyanate wasexpressed in terms of the content (% by weight) of the isocyanate groupsper se in non-blocked form.

The following measurements [A] and [B] were performed, and the contentof blocked polyisocyanate groups was determined in accordance with thefollowing formula:

    The content of blocked isocyanate groups (% by weight)=(a)-(b).

[A] The content (% by weight) of all isocyanate groups in a blockedpolyisocyanate was determined as follows.

About 2 to 5 g of a blocked polyisocyanate was accurately weighed andtaken as a sample. 20 ml of toluene and 20 ml of a 2N solution ofdiethylhexylamine in toluene were added to the sample blockedpolyisocyanate. The resultant was allowed to stand at 60 to 120° C. forseveral tens of minutes to several hours, and then subjected to backtitration using 1N hydrochloric acid at room temperature. UsingBromocresol Green as an indicator, the content (a) of all isocyanategroups in the blocked polyisocyanate was determined in accordance withthe following formula:

    The content (% by weight) (a) of all isocyanate groups={(titer of blank titration)-(titer of sample titration)}×42/{(weight (g) of sample×1000}×100.

The titer of blank titration means a titer obtained by conductingtitration in substantially the same manner as mentioned above, exceptthat the blocked polyisocyanate was not used.

[B] The content (% by weight) of non-blocked isocyanate groups in ablocked polyisocyanate was determined as follows.

About 2 to 5 g of a polyisocyanate was accurately weighed and taken as asample. 20 ml of toluene and 20 ml of a 2N solution of n-dibutylamine intoluene were added to the sample polyisocyanate. The resultant wasallowed to stand at room temperature for 15 minutes, and then subjectedto back titration using 1N hydro chloric acid. Using Bromocresol Greenas an indicator, the content (b) of non-blocked isocyanate groups wasdetermined in accordance with the following formula:

    The content (% by weight) (b) of non-blocked isocyanate groups={(titer of blank titration)-(titer of sample titration)}×42/{weight (g) of sample×1000}×100.

The titer of blank titration means a titer obtained by conductingtitration in substantially the same manner as mentioned above, exceptthat the blocked polyisocyanate was not used.

(10) Hydroxyl Value of Polyol:

The hydroxyl value of a polyol was defined as the amount (mg) of KOHwhich was required for neutralizing acetic acid necessary foracetylation of free OH groups contained in 1 g of the polyol.

Measurement of the hydroxyl value of a polyol was conducted according toJIS-K0070.

(11) Acid Value of Polyol:

The acid value of a polyol was defined as the amount (mg) of KOH whichwas required for neutralizing free fatty acids contained in 1 g of thepolyol.

Measurement of the hydroxyl value of a polyol was conducted according toJIS-K0070.

(12) Solids Content:

The solids content of a polyisocyanate, a blocked polyisocyanate andcoating composition was determined as follows.

About 1.5 g of a sample was accurately weighed, and the sample washeated at 105° C. under atmospheric pressure for 1 hour, whereupon theweight of the sample after heating was measured. The weight of thesample after heating was taken as the amount (weight) of the solids.

REFERENCE EXAMPLE 1

(Production of a polyisocyanate)

A four-necked flask provided with a stirrer, a thermometer, a refluxcondenser, a nitrogen gas feeding pipe and a dropping funnel was purgedwith nitrogen gas. 600 Parts by weight of hexamethylene diisocyanate(HMDI) and 49 parts by weight of a polyether polyol (Adekapolyetherpolyol SP-600, manufactured and sold by Asahi Denka Kogyo K.K., Japan; number average molecular weight: 610; isocyanategroup/hydroxyl group equivalent ratio=15:1) as a hexahydric polyhydroxycompound were charged in the flask, and the resultant was stirred for 9hours while maintaining the internal temperature of the flask at 160°C., to thereby effect a reaction. The resultant reaction mixture wascooled and transferred to a wiped film evaporator, and unreacted HMDIremaining in the mixture was removed, to thereby obtain apolyisocyanate. The obtained polyisocyanate was analyzed by theabove-mentioned methods. As a result, it was found that, with respect tothe polyisocyanate, the viscosity was 6,200 mpa·s at 25° C., theterminal isocyanate group content was 16.9% by weight, the numberaverage molecular weight was 1,940, the average number of terminalisocyanate groups was 7.8, and the cyclic isocyanate trimer content was2.6% by area. It was also found that the allophanate bond concentrationof the polyisocyanate was of degree B.

REFERENCE EXAMPLES 2 TO 7, COMPARATIVE REFERENCE EXAMPLES 1 TO 3

Polyisocyanates were individually prepared in substantially the samemanner as in Reference Example 1 except that the reaction was conductedunder the reaction conditions as shown in Table 1. The unreacted HMDIremaining in the reaction mixture was removed in the same manner as inReference Example 1, to thereby obtain a polyisocyanate. Each of theobtained polyisocyanates was analyzed by the above mentioned methods.Results are shown in Table 1.

COMPARATIVE REFERENCE EXAMPLE 4

A four-necked flask provided with a stirrer, a thermometer, a refluxcondenser, a nitrogen gas feeding pipe and a dropping funnel was purgedwith nitrogen gas. 600 parts by weight of HMDI and 11 parts by weight of1,3-butanediol were charged in the flask, and the resultant was stirredfor 2 hours while maintaining the internal temperature of the flask at80° C., to thereby effect a reaction. Then, the internal temperature ofthe flask was lowered to 60° C., and 0.060 part by weight of tetramethylammonium caprate as a catalyst for forming isocyanurate was added to thereaction mixture. The reaction mixture was intermittently sampled withthe progress of the reaction, and the polyisocyanate content of thesample was determined by measuring the refractive index of the sample.0.073 Part by weight of phosphoric acid was added at the point in timethat the yield of polyisocyanate reached 28% by weight, so that thereaction was terminated. The polyisocyanate-containing reaction mixturewas subjected to filtration, and the unreacted HMDI remaining in thefiltrate was removed by means of a wiped film evaporator, to therebyobtain a polyisocyanate. The obtained polyisocyanate was analyzed by theabove-mentioned methods. Results are shown in Table 1.

COMPARATIVE REFERENCE EXAMPLE 5

A four-necked flask provided with a stirrer, a thermometer, a refluxcondenser, a nitrogen gas feeding pipe and a dropping funnel was purgedwith nitrogen gas. 600 Parts by weight of HMDI and 30 parts by weight ofa polyester polyol "Placcel 303" (manufactured and sold by DicelChemical Industries, Ltd., Japan) as a trihydric alcohol were charged inthe flask, and the resultant was stirred for 1 hour while maintainingthe internal temperature of the flask at 90° C., to thereby effect areaction. Then, the internal temperature of the flask was lowered to 60°C., and 0.060 part by weight of tetramethyl ammonium caprate as acatalyst for forming isocyanurate was added to the reaction mixture. Thereaction mixture was intermittently sampled with the progress of thereaction, and the polyisocyanate content of the sample was determined bymeasuring the refractive index of the sample. 0.073 Part by weight ofphosphoric acid at the point in time that the yield of polyisocyanatereached 54% by weight, so that the reaction was terminated. Thepolyisocyanate-containing reaction mixture was subjected to filtration,and the unreacted HMDI remaining in the filtrate was removed by mean ofa wiped film evaporator, to thereby obtain a polyisocyanate. Theobtained polyisocyanate was analyzed by the above-mentioned methods.Results are shown in Table 1.

                                      TABLE 1                                     __________________________________________________________________________                                Properties of Polyisocyanantes                    Charged materials                Terminal       Cyclic                          (amounts) and NCO/OH   iso-   isocya- Concen-                                         Poly-             Average                                                                            cyanate   Number-                                                                            nate                                                                              tration                     Diisocy- hydroxyl NCO/OH Reaction number of group  average trimer of                                                            allop-                      anate Compound (equi- conditions terminal content Viscosity molecu-                                                             content hanate            (parts    (parts by                                                                           valent                                                                             Temp.                                                                             Time                                                                             isocyanate                                                                         (% by                                                                              (mPa.s                                                                             lar  (% by                                                                             bonds                       by wt.) wt.) ratio) (° C.) (Hr) groups wt.) at 25° C.)                                                            weight area) (degree)     __________________________________________________________________________    Reference                                                                          HMDI SP-600*1                                                                            15   160 9  7.8  16.9  6200                                                                              1940 2.6 B                           Example 1 600 49                                                              Reference HMDI SP-800*2 15 160 9 10.2 17.3  8600 2480 6.1 B                   Example 2 600 49                                                              Reference HMDI HP-1030*3 20 160 2 5.1 13.6  8600 1580 3.1 B                   Example 3 600 67                                                              Reference HMDI HP-2000*4 10 160 3 7.3 8.5 15000 3600 2.5 B                    Example 4 600 250                                                             Reference HMDI HP-1030 10 150 5 7.2 12.0 31000 2520 2.1 B                     Example 5 600 134                                                             Reference HMDI HP-1030 10 170 2 12.2 9.9 53000 3400 2.8 B                     Example 6 600 134                                                             Reference HMDI HP-1030 7.5 160 3 10.1 11.2 86000 3770 0.8 B                   Example 7 600 174                                                             Com- HMDI WR-474*5 5 120 3 5.3 13.2 20000 1690 1.7 B                          parative 600 169                                                              Reference                                                                     Example 1                                                                     Com- HMDI P-400*6 20 120 3 2.2 10.9  1100  840 2.9 C                          parative 600 74                                                               Reference                                                                     Example 2                                                                     Com- HMDI G-400*7 20 120 3 3.2 10.2  2800 1010 1.9 C                          parative 600 74                                                               Reference                                                                     Example 3                                                                     Com- HMDI 1,3- 30  80 2 3.4 21.2  2300  680 40.0  A                           parative 600 butane-   60 4                                                   Reference  diol                                                               Example 4  11                                                                 Com- HMDI Plac- 25  90 1 5.1 19.2  9500 1100 24.0  A                          parative 600 cell303*8   60 4                                                 Reference  30                                                                 Example 5                                                                   __________________________________________________________________________     *1 SP600: hexahydric polyether polyol (manufactured and sold by Asahi         Denka Kogyo K. K., Japan)                                                     *2 SC800: octahydric polyether polyol (manufactured and sold by Asahi         Denka Kogyo K. K., Japan)                                                     *3 HP1030: pentahydric polyether polyol (manufactured and sold by Asahi       Denka Kogyo K. K., Japan)                                                     *4 HP2000: pentahydric polyether polyol (manufactured and sold by Asahi       Denka Kogyo K. K., Japan)                                                     *5 WR474: tetrahydric polyether polyol (manufactured and sold by Asahi        Denka Kogyo K. K., Japan)                                                     *6 P400: dihydric polyether polyol (manufactured and sold by Asahi Denka      Kogyo K. K., Japan)                                                           *7 G400: trihydric polyether polyol (manufactured and sold by Asahi Denka     Kogyo K. K., Japan)                                                           *8 Placcell 303: trihydric polyester polyol (manufactured and sold by         Asahi Denka Kogyo K. K., Japan)                                          

EXAMPLE 1

(Production of a blocked polyisocyanate)

A four-necked flask provided with a stirrer, a thermometer, a refluxcondenser, a nitrogen gas feeding pipe and a dropping funnel was purgedwith nitrogen gas. 100 Parts by weight of the polyisocyanate prepared inReference Example 1 and 32 parts by weight of methyl isobutyl ketonewere charged in the flask. To the resultant mixture was dropwise addedmethyl ethyl ketoxime through the dropping funnel, while maintaining theinternal temperature of the flask at a temperature not exceeding 50° C.,to thereby effect a reaction. The addition of methyl ethyl ketoxime wascontinued until an absorption peak characteristic of an isocyanate groupin the infrared spectrum was no longer observed. Thus a solution of ablocked polyisocyanate (solids content: 80% by weight) was obtained. Theobtained blocked polyisocyanate solution was analyzed according to theabove-mentioned methods, and the analysis showed that, with respect tothe blocked polyisocyante, the average number of blocked terminalisocyanate groups was 7.8, the blocked terminal isocyanate group contentwas 12.5% by weight, based on the weight of the blocked polyisocyanate,and the number average molecular weight of the blocked polyisocyanatewas 2,620.

EXAMPLES 2 TO 7

(Production of blocked polyisocyanates)

Blocked polyisocyanates having a solids content of 80% by weight wereindividually prepared in substantially the same manner as in Example 1,except that the polyisocyanates prepared in Reference Examples 2 to 7were respectively used in these Examples 2 to 7 instead of thepolyisocyanate prepared in Example 1. Each of the obtained blockedpolyisocyanates was analyzed by the above-mentioned methods. Results areshown in Table 2.

COMPARATIVE EXAMPLES 1 TO 5

(Production of blocked polyisocyanates)

Blocked polyisocyanates having a solids content of 80% by weight wereindividually prepared in substantially the same manner as in Example 1,except that the polyisocyanates prepared in Comparative ReferenceExamples 1 to 5 were respectively used in these Comparative Examples 1to 5 instead of the polyisocyanate prepared in Example 1. Each of theobtained blocked polyisocyanates was analyzed by the above-mentionedmethods. Results are shown in Table 2.

                  TABLE 2                                                         ______________________________________                                        Properties of Blocked Polyisocyanates                                                              Terminal                                                   Average number of isocyanate group                                            blocked terminal content Number Average                                       isocyanate groups (wt. %) Molecular Weight                                  ______________________________________                                        Example 1                                                                             7.8          12.5        2620                                           Example 2 10.2 12.7 3370                                                      Example 3 5.1 10.6 2025                                                       Example 4 7.3 7.2 4240                                                        Example 5 7.2 9.6 3150                                                        Example 6 12.2 8.2 4460                                                       Example 7 10.1 9.1 4650                                                       Comparative 5.3 10.4 2150                                                     Example 1                                                                     Comparative 2.2 8.9 1030                                                      Example 2                                                                     Comparative 3.2 8.4 1290                                                      Example 3                                                                     Comparative 3.4 14.7  980                                                     Example 4                                                                     Comparative 5.1 13.7 1540                                                     Example 5                                                                   ______________________________________                                    

EXAMPLE 8

(Evaluation of coating composition obtained using acrylic polyol)

The blocked polyisocyanate prepared in Example 1 and acrylic polyol(Acrydic A-801, manufactured and sold by Dainippon Ink & Chemicals,Inc., Japan; hydroxyl value of the solids content: 100 mg KOH/g; acidvalue of the solids content: 1.5 mg KOH/g; and number average molecularweight: 9,000) were mixed with each other, so that the blockedisocyanate groups/hydroxyl groups equivalent ratio became 1:1, to obtaina mixture. To the resultant mixture was added 0.5% by weight ofdibutyltin dilaurate, based on the total weight of the solids in themixture of the blocked polyisocyanate and the acrylic polyol. For thepurpose of obtaining a coating composition, the resultant mixture wasdiluted with a mixture of ethyl acetate/toluene/butylacetate/xylene/propylene glycol monomethyl ether acetate (weight ratio:30/30/20/15/5) in a dilution ratio such that a coating compostion havinga viscosity of 20 seconds/20° C. as measured by means of a Ford cup #4was obtained. For evaluating the coating composition, the coatingcomposition was sprayed onto a polypropylene plate (size: 50 mm×150 mm),and dried at room temperature for 30 minutes to thereby obtain acoating. The obtained coating was baked at 120° C. for 30 minutes in anoven. With respect to the baked coating, the gel ratio was measured bythe above-mentioned method. Results are shown in Table 3.

EXAMPLES 9 TO 14

Coating compositions were individually prepared in substantially thesame manner as Example 8, except that the blocked polyisocyanatesprepared in Examples 2 to 7 were, respectively, used in these Examples 9to 14 instead of the blocked polyisocyanate prepared in Example 1. Eachof the prepared coating compositions was evaluated with respect to thegel ratio thereof in the same manner as in Example 8. Results are shownin Table 3.

COMPARATIVE EXAMPLES 6 AND 7

Coating compositions were individually prepared in substantially thesame manner as in Example 8, except that the blocked polyisocyanatesprepared in Comparative Examples 2 and 3 were, respectively, used inthese Comparative Examples 6 and 7 instead of the blocked polyisocyanateprepared in Example 1. Each of the prepared coating compositions wasevaluated with respect to the gel ratio thereof in the same manner as inExample 8. Results are shown in Table 3.

REFERENCE EXAMPLE 8

(Production of an epoxy polyol)

A four-necked flask provided with a stirrer, a thermometer, a refluxcondenser, a nitrogen gas feeding pipe and a dropping funnel was purgedwith nitrogen gas. 100 Parts by weight of bisphenol A type epoxy resin(AER6071, manufactured and sold by Asahi-Ciba, K.K. Japan; equivalentamount of epoxy group: 460) and 82 parts by weight of methyl isobutylketone were charged in the flask. To the resultant mixture was dropwiseadded 23 parts by weight of diethanolamine through the dropping funnelover 30 minutes, while maintaining the internal temperature of the flaskat 90° C., to thereby effect a reaction. After the addition ofdiethanolamine, the flask was allowed to stand at 90° C. for 30 minutes.Then, the internal temperature of the flask was raised to 120° C., andthis temperature was maintained for 1 hour. Thus, a solution of an epoxypolyol in methyl isobutyl ketone was obtained. The obtained epoxy polyolsolution was analyzed according to the above-mentioned methods, and theanalysis showed that the solids content of the epoxy polyol solution was60% by weight, based on the weight of the solution, and the hydroxylvalue of the solids (epoxy polyol) was 400 mg KOH/g.

EXAMPLE 15

(Evaluation of a coating composition obtained using epoxy polyol)

The epoxy polyol prepared in Reference Example 8 and the blockedpolyisocyanate prepared in Example 1 were mixed with each other so thatthe equivalent ratio of the blocked isocyanate groups/hydroxyl groups ofthe epoxy polyol became 1:2, to obtain a mixture. To the mixture wasadded 0.5% by weight of dibutyltin dilaurate, based on the total weightof the solids in the mixture of the blocked polyisocyanate and epoxypolyol. The resultant mixture was diluted with methyl isobutyl ketone,so that the content of the solids became 25% by weight, to therebyobtain a coating composition. For evaluating the coating composition,the coating composition was coated onto a tin plate (size: 50 mm×150 mm)using an applicator, and dried at room temperature for 30 minutes tothereby obtain a coating. The obtained coating was baked at 120° C. for30 minutes in an oven. With respect to the baked coating, the gel ratiowas measured by the above-mentioned method. Results are shown in Table3.

EXAMPLES 16 TO 21

Coating compositions were individually prepared in substantially thesame manner as in Example 15, except that the blocked polyisocyanatesprepared in Examples 2 to 7 were, respectively, used in these Examples16 to 21 instead of the blocked polyisocyanate prepared in Example 1.Each of the prepared coating compositions was evaluated with respect tothe gel ratio thereof in the same manner as in Example 15. Results areshown in Table 3.

COMPARATIVE EXAMPLES 8 AND 9

Coating compositions were individually prepared in substantially thesame manner as in Example 15, except that the blocked polyisocyanatesprepared in Comparative Examples 4 and 5 were, respectively, used inthese Comparative Examples 8 and 9 instead of the blocked polyisocyanateprepared in Example 1. Each of the prepared coating compositions wasevaluated with respect to the gel ratio thereof in the same manner as inExample 15. Results are shown in Table 3.

                  TABLE 3                                                         ______________________________________                                        Evaluation of One-Pack Type Urethane Coating Compositions                                                        Gel ratio*                                     of the                                                                       Curing agent prepared                                                         (prepared in Example coating                                                 Main or Comparative composi-                                                  agent Example) tions                                                        ______________________________________                                        Example 8                                                                              A801     Example 1        ⊚                             Example 9 A801 Example 2 ⊚                                     Example 10 A801 Example 3 ⊚                                    Example 11 A801 Example 4 ⊚                                    Example 12 A801 Example 5 ⊚                                    Example 13 A801 Example 6 ⊚                                    Example 14 A801 Example 7 ⊚                                    Comparative A801 Comparative Example 2 x                                      Example 6                                                                     Comparative A801 Comparative Example 3 x                                      Example 7                                                                     Example 15 Epoxy Example 1 ∘                                      Example 16 Epoxy Example 2 ∘                                      Example 17 Epoxy Example 3 ∘                                      Example 18 Epoxy Example 4 ∘                                      Example 19 Epoxy Example 5 ∘                                      Example 20 Epoxy Example 6 ∘                                      Example 21 Epoxy Example 7 ∘                                      Comparative Epoxy Comparative Example 4 x                                     Example 8                                                                     Comparative Epoxy Comparative Example 5 x                                     Example 9                                                                   ______________________________________                                         The gel ratio was determined after curing at 120° C. for 30            minutes.                                                                 

EXAMPLE 22

(Evaluation of impact resistance of coating composition obtained usingpolyester polyol)

The blocked polyisocyanate prepared in Example 4 and polyester polyol(Desmophen 670, manufactured and sold by Bayer Ltd., Germany) were mixedwith each other, so that the blocked isocyanate groups/hydroxy groupsequivalent ratio became 1:1, to obtain a mixture. To the mixture wasadded 0.5% by weight of dibutyltin dilaurate, based on the total weightof the solids in the mixture of the blocked polyisocyanate and thepolyester polyol. The resultant mixture was diluted with the samemixture as used in Example 8, so that the content of the solids became25% by weight, to thereby obtain a coating composition. For evaluatingthe impact resistance of the coating composition, the coatingcomposition was sprayed onto a tin plate (size: 50 mm×150 mm), and driedat room temperature for 30 minutes, to thereby obtain a coating. Theobtained coating was baked at 140° C. for 30 minutes in an oven. Withrespect to the baked coating, the impact resistance was evaluated by theabove-mentioned method to give a degree of ∘.

COMPARATIVE EXAMPLE 10

A coating composition was prepared in substantially the same manner asin Example 22, except that the blocked polyisocyanate prepared inComparative Example 1 was used instead of the blocked polyisocyanateprepared in Example 4. The prepared coating composition was evaluatedwith respect to the impact resistance thereof in the same manner asExample 22, to give a degree of X.

EXAMPLE 23

(Production of adhesive property-imparting composition and evaluation ofthe appearance thereof, and production of plastisol composition usingthe adhesive property-imparting composition and evaluation thereof)

A four-necked flask provided with a stirrer, a thermometer, a refluxcondenser, a nitrogen gas feeding pipe and a dropping funnel was purgedwith nitrogen gas. 100 parts by weight of the polyisocyanate prepared inReference Example 1 and 133 parts by weight of dioctyl phthalate (DOP)were charged in the flask. To the resultant mixture was dropwise addedmethyl ethyl ketoxime (MEKoxime) through the dropping funnel, whilemaintaining the internal temperature of the flask at a temperature notexceeding 50° C., to thereby effect a reaction. The addition of MEKoximewas continued until an absorption peak characteristic of an isocyanategroup in the infrared spectrum was no longer observed. Thus, an adhesiveproperty-imparting composition having a solid content of 50% by weightwas obtained. The appearance of the obtained adhesive property-impartingcomposition was evaluated.

For evaluating the adhesive property of the adhesive property-impartingcomposition, a plastisol composition was obtained, which is a mixture of70 parts by weight of a straight polyvinyl chloride resin (KanevinylPSL-10, manufactured and sold by Kanegafuchi Chemical Industry Co. Ltd.,Japan), 30 parts by weight of a vinyl chloride copolymer (KanevinylPCH-12, manufactured and sold by Kanegafuchi Chemical Industry Co. Ltd.,Japan), 110 parts by weight of DOP, 150 parts by weight of calciumcarbonate, 3 parts by weight of dibasic lead phosphate, and 3 parts byweight of the adhesive property-imparting composition. With respect tothe obtained plastisol composition, the adhesive property was evaluatedby the above-mentioned method. Results are shown in Table 4.

EXAMPLES 24 TO 29

Adhesive property-imparting compositions having a solids content of 50%by weight and plastisol compositions were individually prepared insubstantially the same manner as in Example 23, except that thepolyisocyanates prepared in Reference Examples 2 to 7 were,respectively, used in the Examples 24 to 29 instead of thepolyisocyanate prepared in Reference Example 1. The blocking agents andsolvents were used as shown in Table 4. With respect to each of theplastisol compositions, the adhesive property was evaluated by theabove-mentioned method. Results are shown in Table 4.

EXAMPLE 30

A four-necked flask provided with a stirrer, a thermometer, a refluxcondenser, a nitrogen gas feeding pipe and a dropping funnel was purgedwith nitrogen gas. 100 parts by weight of polyisocyanate prepared inReference Example 1 and 187 parts by weight of DOP, 95 parts by weightof nonylphenyl and 0.0191 part by weight of dibutyltin dilaurate werecharged in the flask. The internal temperature of the flask wasmaintained at 80° C. for 6 hours, to thereby obtain an adhesiveproperty-imparting composition having a solids content of 50% by weight.A plastisol composition was prepared in the same manner as in Example23, except that the above-obtained adhesive property-impartingcomposition was used instead of the adhesive property-impartingcomposition prepared in Example 23. With respect to the plastisolcomposition, the adhesive property was evaluated by the above-mentionedmethod. Results are shown in Table 4.

COMPARATIVE EXAMPLES 11 TO 13

Adhesive property-imparting compositions having a solids content of 50%and plastisol compositions were prepared in substantially the samemanner as in Example 23, except that the polyisocyanates prepared inComparative Reference Examples 2 to 4, were, respectively, used in theComparative Examples 11 to 13 instead of the polyisocyanate prepared inReference Example 1. With respect to each of the plastisol compositions,the adhesive property was evaluated by the above-mentioned method.Results are shown in Table 4.

                                      TABLE 4                                     __________________________________________________________________________    Materials for adhesive property-imparting                                       compositions and evaluation thereof Evaluation                              Polyisocyanate                  of Plastisol                                    Prepared in Blocking Solvent  com-                                            Reference Example or agent DOP  positions                                     Comparative Example (parts by (parts  Adhesive                                (parts by wt.) wt:) by wt.) Appearance Property                             __________________________________________________________________________    Example 23                                                                          Reference Example 1                                                                     MEKoxime                                                                            133 Uniform &                                                                           ◯                                    100 37  transparent                                                          Example 24 Reference Example 2 MEKoxime 134 Uniform & ◯                                           100 38  transparent                           Example 25 Reference Example 3 MEKoxime 126 Uniform & ◯                                           100 30  transparent                           Example 26 Reference Example 4 MEKoxime 118 Uniform & ◯                                           100 18  transparent                           Example 27 Reference Example 5 MEKoxime 124 Uniform & ◯                                           100 26  transparent                           Example 28 Reference Example 6 MEKoxime 120 Uniform & ◯                                           100 22  transparent                           Example 29 Reference Example 7 MEKoxime 122 Uniform & ◯                                           100 24  transparent                           Example 30 Reference Example 1 Nonyl- 187 Uniform & ◯                                             100 phenyl  transparent                         95                                                                          Comparative Comparative MEKoxime 122 Uniform & X                              Example 11 Reference Example 2 24  transparent                                 100                                                                          Comparative Comparative MEKoxym 120 Uniform & X                               Example 12 Reference Example 3 22  transparent                                 100                                                                          Comparative Comparative MEKoxym 142 Phase not                                 Example 13 Reference Example 4 46  separation determined                       100                                                                        __________________________________________________________________________

INDUSTRIAL APPLICABILITY

According to the present invention, there is provided a novel blockedpolyisocyanate obtained by blocking the terminal isocyanate groups of anon-blocked polyisocyanate with a thermally dissociative blocking agent,wherein the non-blocked polyisocyanate is obtained by reacting at leastone diisocyanate selected from the group consisting of an aliphaticdiisocyanate and an alicyclic diisocyanate with a polyhydroxy compoundhaving an average number of hydroxyl groups as many as 4.5 to 10, andremoving substantially all unreacted diisocyanate monomers. The use ofthe blocked polyisocyanate of the present invention includes, forexample, a coating composition comprising a polyol as a main agent andthe blocked polyisocyanate as a curing agent; an adhesiveproperty-imparting composition comprising the blocked polyisocyanate,and a plasticizer and/or a solvent which are/is for the blockedpolyisocyanate; and a plastisol composition comprising a plastisol(which is a dispersion of a vinyl chloride polymer in a plasticizer),and the adhesive property-imparting composition. The coating compositioncomprising the blocked polyisocyanate of the present invention as acuring agent not only has excellent curability even under lowtemperature conditions, but is also capable of forming a coating whichhas excellent impact resistance. Therefore, the coating composition ofthe present invention can be advantageously used for coating a metallicsubstrate (such as a steel plate or a surface-treated steel plate) and aplastic substrate, by the technique of roll coating, curtain flowcoating or the like. Especially, the coating composition of the presentinvention is useful as materials for undercoating, top coating andintercoating various substrates; a coating material for a precoatedmetal including a rust-resistant steel plate; and a coating material forimparting fine appearance, weatherability, acid resistance, rustresistance, mechanical strength (such as chipping resistance and impactresistance) and the like to automobiles. The blocked polyisocyanate ofthe present invention has excellent miscibility with a plasticizer forthe blocked polyisocyanate, so that, an adhesive property-impartingcomposition comprising the blocked polyisocyanate and a plasticizerand/or a solvent can be combined with a plastisol to prepare a plastisolcomposition having excellent adhesive properties even under lowtemperature conditions. This plastisol composition can be advantageouslyused, for example, as sealants, materials for forming an undercoatingand a chip-resistant coating, and a material for the preparation of aPVC-coated steel plate in the fields of automobiles, wherein theplastisol composition is applied to a substrate by the technique ofspraying, brushing or the like.

What is claimed is:
 1. A blocked polyisocyanate, which is substantiallythe same product as obtained by blocking 50 to 100% by mole of theterminal isocyanate groups of a non-blocked polyisocyanate with athermally dissociative blocking agent, said non-blocked polyisocyanatebeing obtained by reacting at least one diisocyanate selected from thegroup consisting of an aliphatic diisocyanate and an alicyclicdiisocyanate with a polyhydroxy compound having an average number ofhydroxyl groups of from 4.5 to 10, and removing substantially allunreacted diisocyanate monomers,said non-blocked polyisocyanate havingthe following characteristics (a) to (d):(a) a cyclic isocyanate trimercontent of 10% or less, in terms of a ratio of the area of a peakascribed to a cyclic isocyanate trimer, relative to the total area ofall peaks ascribed to said non-blocked polyisocyanate in a gelpermeation chromatogram thereof; (b) an average number of terminalisocyanate groups of from 5 to 20; (c) a number average molecular weightof from 1,200 to 10,000 as measured by gel permeation chromatography(GPC); and (d) a terminal isocyanate group content of from 5 to 20% byweight, said blocked polyisocyanate having the following characteristics(e) to (g):(e) an average number of blocked terminal isocyanate groupsof from 5 to 20; (f) a blocked terminal isocyanate group content of from2 to 20% by weight; and (g) a number average molecular weight of from1,500 to 15,000 as measured by GPC.
 2. The blocked polyisocyanateaccording to claim 1, wherein said polyhydroxy compound is selected fromthe group consisting of a polyether polyol, a polyester polyol and amixture thereof.
 3. The blocked polyisocyanate according to claim 2,wherein said polyhydroxy compound is a polyether polyol to which atleast one organic oxide selected from the group consisting of alkyleneoxides and phenylalkylene oxides is addition-bonded.
 4. The blockedpolyisocyanate according to claim 3, wherein said alkylene oxide isselected from ethylene oxide, propylene oxide, butylene oxide andcyclohexene oxide, and said phenylalkylene oxide is selected fromstyrene oxide and phenylpropylene oxide.
 5. The blocked polyisocyanateaccording to claim 4, wherein said polyhydroxy compound is a polyetherpolyol to which propylene oxide is addition-bonded.
 6. The blockedpolyisocyanate according to claim 1, which has an allophanate bond in amolecule thereof.
 7. The blocked polyisocyanate according to claim 1,wherein said thermally dissociative blocking agent is selected from thegroup consisting of an alkylphenol compound, an oxime compound, an acidamide compound, an active methylene compound and a mixture thereof.
 8. Acoating composition comprising:(A) a polyol having a hydroxyl value offrom 10 to 500 mg KOH/g, an acid value of from 0 to 200 mg KOH/g, and anumber average molecular weight of from 300 to 60,000; and (B) a blockedpolyisocyanate of any one of claims 1 to
 7. 9. The coating compositionaccording to claim 8, wherein said polyol is selected from the groupconsisting of an aliphatic hydrocarbon polyol, a polyether polyol, apolyester polyol, an epoxy polyol, a fluoropolyol, an acrylic polyol anda mixture thereof.
 10. An adhesive property-imparting compositioncomprising a blocked polyisocyanate of any one of claims 1 to 7 and atleast one member selected from the group consisting of a plasticizer forsaid blocked polyisocyanate and a solvent for said blockedpolyisocyanate.
 11. A plastisol composition comprising a plastisol andan adhesive property-imparting composition of claim 10.